A lithography process for semiconductor manufacturing uses a lithography system which projects and exposes a circuit pattern formed on a mask to a photoresist applied to a wafer.
FIG. 7 is a plan view showing the schematic arrangement of a conventional lithography system. A lithography system 100 has a master transport apparatus 130 for transporting a mask, a prealignment device 107, and an exposure section 120.
The master transport apparatus 130 is constituted by a library 103, cassette transport device 105, cassette opening/closing unit 104, mask transport mechanism 108, inspection device 106, controller (control section) 111, and the like. A mask 101 is accommodated in a cassette 102 which can be opened and closed, and is kept in stock in the library 103 which has a plurality of slots for storing masks 101.
The cassette transport device 105 transports the cassette 102 between the library 103 and opening/closing unit 104. The cassette transport device 105 can be constituted by, e.g., a cassette holding hand 105a, and a scalar type tri-articulated robot mechanism 105b which drives the hand 105a in R, θ, and Z directions (R is a radial direction, θ is a rotational direction within a horizontal plane, and Z is a vertical direction).
The opening/closing unit 104 has a plurality of slots for holding cassettes 102, a driving mechanism for driving an arbitrary slot to a predetermined height, and an opening/closing mechanism for opening/closing a cassette in a slot driven to the predetermined height (i.e., a target cassette from and to which a mask is to be unloaded and loaded).
The inspection device 106 has an inspection table (not shown), and measures particles attaching to a pellicle (not shown) adhered to the pattern surface side of the mask 101 placed on the inspection table and to the respective surfaces of the blank of the mask 101.
The prealignment device 107 prealigns (roughly aligns) the mask 101 before it is provided to a mask stage (master stage) 109.
The mask transport mechanism 108 has one holding hand 108a, and a tri-articulated robot 108c for extending/contracting the holding hand 108a, and transports the mask 101 among the cassette opening/closing unit 104, inspection device 106, and prealignment device 107.
The exposure section 120 has the mask stage (master stage) 109 which receives and holds the mask 101 prealigned by the prealignment device 107, a mechanism which finely aligns the mask 101 held on the mask stage 109, an illumination system which illuminates the mask 101, a projection system which projects the pattern of the mask 101, a wafer stage which positions a wafer (substrate), and the like, and exposes the wafer with the pattern of the mask 101.
A mask manipulating mechanism 110 has two holding hands 110a and 110b. The mask manipulating mechanism 110 holds the mask 101 with the hands 110a and 110b, and transports the mask 101 or exchanges two mask 101 between the prealignment device 107 and reticle stage 109.
The mask manipulating mechanism 110 may transport the mask 101 or exchange the two masks 101 by rotating a turntable. More specifically, the mask manipulating mechanism 110 may have first and second holding portions 110a and 110b on its turntable. According to this arrangement, for example, the first holding portion 110a holds a mask used, and the second holding portion 110b holds a mask to be used next (prealigned mask). In this state, the turntable is rotated, so that the first and second holding portions 110a and 110b are rotated (revolve) through 180° about their middle point as the center. Thus, the mask used and held by the first holding portion 110a can be unloaded from the mask stage 109 to the prealignment stage of the prealignment device 107, and the mask held by the second holding portion 110b, which is to be used next, can be loaded from the prealignment stage to the mask stage 109.
When exposure of the mask using the mask 101 is ended, the mask 101 used is transported to the prealignment device 107 by the manipulating mechanism 110. After that, the mask 101 used is accommodated in the corresponding cassette in the cassette opening/closing unit 104 by the transport mechanism 108. A mask 101 to be used next is extracted from a cassette in the cassette opening/closing unit 104 by the transport mechanism 108, and is transported to the inspection device 106, so that any foreign substance on it is inspected. The inspected mask 101 is transferred to the prealignment device 107 by the transport mechanism 108.
In the production of system LSIs or the like, the lot size decreases, and accordingly the mask exchange frequency increases, so that reduction in the mask exchange time accompanying mask exchange is sought for.
Demand has arisen for multiple exposure (a technique of forming a finer circuit by printing the circuit patterns of a plurality of masks in an overlaying manner) which is becoming popular as a micropatterning technique. To meet this demand in multiple exposure, the existing system has, e.g., the following problems. In the case of double exposure, it takes a long period of time to transport a mask which is to be used next. This produces a waiting time on the mask stage and decreases the rate of operation of the apparatus. In the case of triple exposure, to expose one wafer, at least one mask must be stored in the mask cassette. Accordingly, the possibility of contaminating the mask increases, and attaching of a foreign substance to the mask must be inspected again. This increases the mask exchange time and decreases the throughput largely. Demand has arisen for minimizing a decrease in throughput in multiple exposure as well as the contamination risk for the mask which is to be reused.